Movable liner assembly for a deposition zone in a cvd reactor

ABSTRACT

A chemical vapor deposition (CVD) reactor comprises a deposition zone, a substrate carrier and a liner assembly. The deposition zone is constructed so as to have a positive pressure reactant gases fixed showerhead introducing reactant gas supporting thin film CVD deposition. The substrate carrier movably supports a substrate and the liner assembly within the deposition zone and is heated so as to be subjected to a CVD process. The liner assembly partly encloses selected portions of the deposition zone, particularly portions of the substrate carrier and thereby enclose a hot zone surrounding a substrate to be processed so as to retain heat in that zone but allows gas flow radially outwardly toward walls of a surrounding cold-wall reactor with exhaust ports surrounding the deposition zone that exhaust spent reactant gases. The liner assembly is a sink for solid reaction byproducts while gaseous reaction byproducts are pumped out at the exhaust ports. The liner assembly is linearly movable away from the fixed showerhead.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No.13/222,881, entitled “Movable Liner Assembly for a Deposition Zone in aCVD Reactor,” filed on Aug. 31, 2011, which is incorporated herein itsentirety by this reference.

TECHNICAL FIELD

The present invention relates to chemical vapor deposition thin-filmdeposition reactors, and relates particularly to protective liners thatmay be provided in such deposition reactors.

BACKGROUND ART

Chemical vapor deposition (CVD) processes use induced chemical reactionsof gaseous precursor molecules to deposit one or more thin-film layersonto the surface of a substrate. For example, a trimethylgallium andarsine reaction induced by a combination of elevated temperature andradio frequency energy can be used to produce a gallium arsenide filmlayer. A wide variety of CVD precursor substances are known.

Frequently encountered challenges involving CVD reactors includeuniformity of deposition, contamination issues, and downtime for reactormaintenance affecting throughput. Uniformity of deposition requires acorresponding uniformity of reactor environment conditions in thevicinity of substrate surface being processed, including uniformreaction gas mixture and concentration and uniform temperature. Ideally,deposition will occur only on the surface of the substrate beingprocessed, with such deposition being substantially uniform over thatsubstrate. In practice, unwanted deposition (as well as precursorcondensation) may occur also on some surfaces of the reactor itself thatare exposed to the precursor molecules or intermediate reaction productsunder conditions that allow deposition. When surface deposits build upin the reactor, material can break off to introduce contaminantparticles to the reactor environment. The surface build-up can alsoadversely affect processing conditions that may lead to decreaseddeposition rates onto the substrate or deposition non-uniformity. Tohandle these issues, the reactor must be periodically cleaned to removeany unwanted depositions from the reactor surfaces, which leads in turnto reactor downtime and reduced throughput.

SUMMARY

A chemical vapor deposition (CVD) reactor in accord with the presentinvention comprises a gas and heat isolated deposition zone protected bya movable liner assembly that partially shrouds the deposition zonewithin conventional reactor housing, over a workpiece, thereby forming avirtual reactor within a conventional reactor. The liner is movablebecause it is associated with a moving carrier but a stationaryshowerhead, so that the liner can be cleaned and replaced away from thedeposition zone. The deposition zone is constructed so as to provide apositive pressure reactive gas first environment supporting thin filmdeposition thermally isolated from a surrounding lower pressure andenergy providing second environment. A movable substrate carrier isconstructed to support a substrate within the deposition zone so as tobe subjected to a CVD process in the deposition zone. The liner assemblyis made of a liner material with liner walls that are positioned so asto form inner and outer partial enclosures or shrouds that help toensure uniformity of deposition such that the inner partial enclosure isprotected within the outer partial enclosure. The liner assembly forms ahot zone surrounding a substrate to be processed so as to retain heat inthat zone and also maintains a concentration of process gas in proximityto the substrate. A result is that the substrate receives good filmdeposition. The liners also protect selected portions of the depositionzone from any unwanted film deposition. Such a deposition zone may behoused in a larger cold-wall reactor that provides a lower pressuresecond environment, plus access ports for substrates when the substratesare mounted on a linearly movable carrier that transports substrates outof the deposition zone.

The liner assembly may include a first set of liners forming an outergas flow tunnel-like enclosure of the deposition zone with first outerside walls adapted to minimize heat loss from regions receiving the CVDprocess gas, as well as an inner deposition liner within that outerenclosure defined by the first set of liners. The inner deposition linerhas second liner side walls that partially enclose a hot reaction zoneimmediately surrounding a perimeter of the substrate, except for anopening at the top provided to receive the CVD process gas. For example,the liner assembly may line any of (1) regions surrounding openings of aCVD process showerhead of the deposition zone, (2) a region immediatelysurrounding a location of the substrate (i.e., the hot zone defined bythe inner liner) where spent reactant gas flows radially outwardlythrough the gas flow tunnel, and (3) gas isolation regions separating aconcentration of CVD process gas in the deposition zone above thesubstrate from regions outside of the deposition zone in the nature ofgas curtains surrounding deposition zones.

Portions of the liner assembly of the first environment may be inthermal communication with a heat source of the second environment so asto be maintained at an elevated temperature higher than the substrate.The liner material may be made from any of quartz, a ceramic, and/orgraphite, which retain heat. The liner material is also preferablyresistant to selected cleaning processes, such as etchants, that removedeposited material. Additionally, the liner assembly or portions thereofmay be selectively removable from the deposition zone for replacement.

The carrier is supported on spaced apart rollers such that the carrierslides in a linear path. In this manner, one liner assembly can be movedaway from a fixed showerhead while another liner assembly is placedbelow the showerhead. Such a structure allows assembly line depositionof substrates, one after another.

In one embodiment, a substrate carrier may support a plurality of wafersubstrates for simultaneous processing by a plurality of showerheads.The plurality of wafer substrates may be arranged in one or more groups,each having a showerhead and associated liners.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway side view of a CVD reactor in accord with thepresent invention.

FIG. 2 is an enlarged view of a deposition zone of the reactor of FIG.1, indicated by circle A, showing the presence of liners in accord withthe present invention.

FIGS. 3 and 4 are cutaway perspective views of a deposition zone of thereactor of FIG. 1, respectively from above and below a substrate to betreated, and showing the various liners of the liner assembly.

FIG. 5 is a cutaway side view of an alternative CVD reactor withmultiple deposition zones accommodating the processing of multiplesemiconductor substrates or wafer substrates at one time.

FIG. 6 is a top view of a substrate carrier with multiple substrates forprocessing in the reactor of FIG. 5.

DETAILED DESCRIPTION

With reference to FIG. 1, a CVD cold-wall reactor 11 is provided with adeposition zone 21 that is constructed so as to enclose an environmentsupporting thin film deposition onto a substrate. In particular, one ormore process gas inlets 17 are provided for supplying gaseous CVDprecursors via a showerhead assembly 19 toward a substrate 29 within thereactor 11, while one or more exhaust outlets is provided for removingany excess process gas and reaction products from the chamber 21. Amovable carrier 25 receives and transports a substrate to be processedinto the deposition zone 21, where it can be subject to any known CVDprocess. In FIG. 1, the carrier 25 moves out of the plane of the drawingon opposed rollers 36, 38. The deposition zone 21 may be considered as acentral reactor within the larger cold-wall reactor 11 that provides thelow pressure or vacuum environment for the deposition zone 21, substrateaccess ports, heating and cooling sources, radio frequency energy andsubstrate rotation if needed. Such cold-wall reactors are commerciallyknown. A typical film to be deposited is a gallium arsenide film.Precursor gases are typically trimethyl gallium and arsine.

As seen in the enlarged view of the deposition zone 21 in FIG. 2, thecarrier track 25 holds an oversized wafer susceptor 27 supporting awafer substrate 29 thereon. The carrier 25 may be transparent material,such as fused silica or quartz, and the susceptor 27 may be preferablyconstructed from graphite material to form a thermal susceptor that isradiantly heatable by a set of lamps 28 located beneath the transparentcarrier 25. The wafer substrate 29 may be heated by thermal conductionfrom the heated susceptor 27 on which it sits. The wafer carrier 27 andwafer substrate 29 are received by the carrier 25 into the depositionzone 21, e.g. through a port in the reactor 11, and likewise exits thedeposition zone 21 through the same or a different port. The reactor 11may include multiple processing and/or inspection chambers connected toeach other through such ports, with the carrier 25 facilitatingtransport of a substrate on a wafer carrier between such chambers.

Within a portion of the chamber 21, a CVD hot zone is created as a firstenvironment where CVD precursor gases 24 supplied to the chamber 21 bythe showerhead assembly 19 through a plurality of apertures, not shown,react to form CVD reaction products that are formed on a substrate 29present in the hot zone. In accord with the present invention, abox-like liner assembly comprising a plurality of stacked liners 33, 35,and 37 are provided so as to enclose the hot zone and thereby maintain auniform temperature above the substrate 29. Liner 35 has legs 36 thatsupport the liner from carrier 25. That is, the liner assembly forms atleast one box around the substrate 29, creating the hot zone with smallopenings for radially outward gas flow. A first set of liners 33 and 35may be arranged to form an outer box enclosure of that portion of thechamber 21 receiving the CVD precursor gases, with chamber lid liner 35forming first outer side walls of that outer box enclosure, while thedeposition liner 37 may form an inner enclosure, with second inner sidewalls of the deposition liner 37 immediately surrounding portions of theperiphery of the substrate 29. The liner material may be any of quartz,a ceramic, and graphite, which retain heat. The liners 33, 35 and 37receive their heat generally by convection from the flowing CVD gasesand reaction products, but mostly from energy supplied by radiation fromthe hot carrier 27 and substrate 29.

The substrate 29 may itself be heated by conduction from the susceptor27, which in turn may be heated by lamps, electrical induction, fluidpassages, or any other convenient means in the cold-wall reactor, i.e.,the second environment. The CVD precursor gases are preferably deliveredto the hot zone already preheated to an elevated temperature (e.g.,about 350° C.) just below a reaction temperature, and is then heated toits final reaction temperature (e.g., about 400 to 450° C.) fordeposition by heat transfer onto the substrate 29 where CVD reactionsoccur. The surrounding inner liner material 37 maintains the heat in hotzone immediately above the substrate 29, like the walls of an oven, forcreating conditions conducive to uniform deposition by reactions on thesubstrate 29. By maintaining the deposition zone at 400° C. or hotter,excess arsenic remains in a gaseous phase so that it can be pumped outthrough an exhaust port. Excess gallium tends to plate out onto theliners. At lateral edges of the showerhead, gas exhaust ports 34 and 38may be provided to form part of a gas flow curtain around theshowerhead. Such a gas flow curtain partly isolates the reaction chamberhelping to form a reactor within a reactor, as explained further below.

Additionally, the liners 33, 35 and 37 of the liner assembly arepositioned to line selected portions of the deposition zone 21 so as tocontrol byproducts of the CVD reaction during deposition and protectthose selected portions of the chamber 21 from unwanted film deposition.Management of deposition byproducts and temperature control are theprincipal functions of the liner assembly. Thus, a showerhead liner 33protects a first zone of the deposition zone 21 surrounding the CVDprocess gas outlets 31 of the showerhead assembly 19. The showerhead.liner 33 minimizes loss of heat from the showerhead assembly 19 toprevent condensation of preheated CVD precursor gases in the showerheadchannels and especially at its gas outlets 31. A chamber lid liner 35protects a third zone of the deposition zone 21 outside of thedeposition zone. It physically separates a concentration of the CVDprocess gas and reaction products in a hot deposition zone above thewafer substrate 29 from cooler isolation regions outside of thedeposition zone. Additionally, pressure differences between thedeposition zone and isolation regions may produce radially outward gasflows that direct any unreacted process gas and undeposited reactionproducts to an exhaust port of the chamber 21, such as an exhaust port34 or 38. Finally, a deposition liner 37, in addition to forming aninner hot zone of the deposition zone 21, protects portions of theoversized wafer carrier 27 around the wafer substrate 29.

At least some portions of the liner assembly may be in thermalcommunication with one or more heat sources (radiant, convective, orconductive) so as to be maintained at an elevated temperature differentfrom than the substrate so as to discourage deposition anywhere otherthan onto the wafer substrate 29. Even so, some deposition and/orcondensation may occur onto the liners 33, 35 and 37. Accordingly, thepreferred liner materials (e.g., quartz, a ceramic, or graphite), inaddition to retaining heat, are preferably selected so as to beresistant to various cleaning processes. The liners are preferablyremovable from the reaction chamber for maintenance or replacement. Thedeposition liner 37 nearest to the wafer substrate 29 is especiallydesigned to be removable along with the substrate 29 and its susceptor27 after each substrate processed. The reaction chamber with its gascurtain isolation provides a reduction in contaminants that is at leastan order of magnitude less than in the surrounding reactor environment.

With reference to FIGS. 3 and 4, cutaway perspective views with theshowerhead assembly 19 removed reveal the showerhead liner 33 surroundedby one or more plates of a chamber lid liner 35 overlying a susceptor 27and carrier 25 carrying a wafer substrate 29. The showerhead liner 33,which generally corresponds in its location, shape and size with that ofthe showerhead assembly's process gat inlet, overlays the processinglocation of a wafer substrate 29 inserted into the reactor. The chamberlid liner 35 surrounds the showerhead liner 33. In the depictedembodiment, the chamber lid liner 35 is seen to have legs 36 extendingdownward along the sides of the susceptor 27 onto the carrier 25.Alternatively, the legs 36 could be replaced by side panels. In eithercase, the legs 36 or side panels form a tunnel or cap with the chamberlid liner 35 around the deposition zone that both confines processreaction gas and minimizes heat loss in the lateral direction, yetallows excess or spent gas to flow out. A deposition liner 37 seated onthe susceptor 27 and the movable carrier surrounds a perimeter of thewafer substrate 29 so as to form a kind of partial inner “box” or“dome”, with the fixed showerhead liner 33 forming the box or dome'scover and the deposition liner 37 defining its side walls on all sidesof the wafer substrate 29. The deposition liner therefore ensurestemperature and process gas uniformity over the wafer substrate surface.

With reference to FIGS. 5 and 6, another CVD reactor embodiment 61illustrates the possibility of scaling to accommodate the processing ofmultiple wafer substrates 79A1-79D4 at one time, while still maintainingthe use of liners for promoting deposition uniformity. The illustratedembodiment provides for 16 wafer substrates, shown here as grouped intofour sets of four, 79A1-79A4, 79B1-79B4, 79C1-79C4 and 79D1-79D4.Different numbers of wafers and different groupings are possible in avariety of reactor embodiments. Each set of wafers has an associatedshowerhead, of which showerheads 69A and 69B are seen in FIG. 5. Theshowerheads are connected to one or more supplies of process gases,represented by conduits 67. Each of the showerheads has a showerheadliner, e.g., 83A and 83B, and the showerhead liners are in turnsurrounded by one or more plates forming a chamber lid liner 87 withside panels or legs 86 at lateral sides of each deposition zoneassociated with a group of wafers, such that the combination ofshowerhead liners and chamber lid liners forms a tunnel or cap aroundthe respective deposition zones that both confine process gas andminimizes heat loss in the later direction. Additionally, each group ofwafer substrates 79A1-79A4, 79B1-79B4, 79C1-79C4, and 79D1-79D4, has acorresponding deposition liner 85A-85D positioned on the movable wafercarriers 77A-77D surrounding the parameter of each group. In combinationwith the showerhead liners, the deposition liners form a kind of partialinner box or dome around the wafer substrates that ensure temperatureand process gas uniformity over each wafer substrate surface and isolateone environment from another. The movable carriers allow linerassemblies to be moved away from fixed showerheads for cleaning.

The reactor structure provided by the present invention allows betteruniformity of deposition by creating an environment where the substratehas uniform temperature over its entire surface and where the CVDprocess gases over the substrate are likewise at a uniform temperaturein a hot zone. The regions or zones enclosed by the various sets ofliners facilitate heat retention for such temperature uniformity, whilethe liners themselves also serve to protect selected portions of thechamber from unwanted deposition and to facilitate short downtimes forcleaning and maintenance.

What is claimed is:
 1. A method for chemical vapor deposition (CVD) ofthin films, comprising: providing a deposition zone in a reactionchamber, the reaction chamber having a fixed showerhead assembly thatintroduces CVD reactive gases under positive pressure into thedeposition zone; moving a substrate carrier beneath the showerheadassembly in the reaction chamber, the substrate carrier beingconstructed to support and transport at least one substrate within thereaction chamber so as to be subjected to a CVD process by the CVDreactive gases; providing a liner assembly shrouding the deposition zoneand including at least one partial enclosure around the deposition zoneisolating the deposition zone and the substrate carrier, whereby solidreaction byproducts are plated onto material in the liner assembly andgaseous reaction byproducts flow radially outward, the liner assemblybeing mounted on the substrate carrier for motion with the substratecarrier, and wherein the at least one partial enclosure of the linerassembly includes: a chamber lid liner and a showerhead liner in a shapeof an outer tunnel enclosure of the deposition zone, and a depositionliner within and beneath the outer tunnel enclosure formed by thechamber lid liner and the showerhead liner; maintaining a depositionzone temperature in the deposition zone during the CVD process;depositing a thin film onto a surface of the at least one substrate aspart of the CVD process; exhausting the radially outwardly flowinggaseous reaction byproducts at the periphery of the reaction chamber;and moving the substrate carrier with the at least on substrate out ofthe deposition zone.
 2. The method of claim 1, wherein the chamber lidliner includes a plate and a pair of legs that are directly disposed onthe substrate carrier at lateral sides of the plate, the plate extendingfrom the legs along a length perpendicular to the legs and parallel to alength of the substrate carrier, the showerhead liner surrounded by theplate and overlaying a substrate processing location, and the outertunnel enclosure adapted to minimize heat loss from regions receivingthe CVD reactive gases.
 3. The method of claim 1, wherein the depositionliner is separate from the chamber lid liner and the showerhead liner,walls of the deposition liner being directly positioned on a susceptorheld by the substrate carrier and surrounding all sides of the at leastone substrate, thereby protecting portions of the substrate carrieraround the at least one substrate, the outer tunnel enclosure allowinggas to flow radially outwardly.
 4. The method of claim 1, furthercomprising providing a radiant and convective energy within the reactionchamber for maintaining the deposition zone temperature.
 5. The methodof claim 4, wherein: the substrate carrier is transmissive of theradiant and convective energy, and the radiant and convective energy isprovided by a lamp source to the at least one substrate through thesubstrate carrier.
 6. The method of claim 1, further comprisingintroducing the CVD reactive gases by the fixed showerhead assembly intothe deposition zone at a first temperature and heating the CVD reactivegases to a second temperature at the deposition zone, the secondtemperature being higher than the first temperature.
 7. The method ofclaim 1, wherein the first temperature is 350° C. and the secondtemperature is between 400° C. and 450° C.
 8. The method of claim 1,wherein maintaining the deposition zone temperature in the depositionzone includes maintaining the deposition zone temperature at 400° C. ora higher temperature.
 9. The method of claim 1, further comprisingremoving the deposition liner along with the at least one substrate anda susceptor held by the substrate carrier after the deposition of thethin film onto the surface of the at least one substrate.
 10. The methodof claim 1, wherein material for at least a portion of the linerassembly is one of quartz, a ceramic, or graphite.
 11. The method ofclaim 1, further comprising providing gas curtain regions surroundingoutlets of the showerhead assembly.
 12. The method of claim 1, whereinmoving the substrate carrier beneath the showerhead assembly includesmoving the substrate carrier in a linear motion over a rollers in thereaction chamber.
 14. The method of claim 1, wherein moving thesubstrate carrier out of the deposition zone includes moving thesubstrate carrier in a linear motion over a rollers in the reactionchamber.
 15. The method of claim 1, wherein: moving the substratecarrier beneath the showerhead assembly includes moving the substratecarrier into the reaction chamber through a port, and moving thesubstrate carrier out of the deposition zone includes moving thesubstrate carrier out of the reaction chamber through the port orthrough a different port.